PGP and breast cancer: Despite having different pharmacological activities, macrolide compounds are substrate of P-gp [32], in particular the antitumor effects of everolimus and sirolimus are well documented as inhibitors of cellular proliferation through mTOR (mammalian target of rapamycin) inhibition in some tumor models such as renal cell carcinoma, hepatocellular carcinoma and breast cancer [33,34].